The traditional method for transporting and storing drums or barrels in commerce utilizes various forms of pallets upon which the drums or barrels are stacked, the latter two terms of the art being illustrative of containers and these terms being used interchangeably herein. Conventionally, such containers are in the shape of a right circular cylinder, but need not be so. Thus, containers can be easily and efficiently moved about in locations such as a warehouse, a trailer, a loading dock, a factory floor, and the like, using a fork-lift truck. Conventional pallets for this purpose have been traditionally made of wood, largely based on its relative availability, strength and modest cost. However, wood pallets suffer from drawbacks such as poor resistance to chemical spills and rotting/warpage due to environmental exposure, and they do not provide any constraint for drums under high vibration conditions. Therefore, several modern designs have focused on the use of plastic pallets in an attempt to overcome some of the above disadvantages. Advances in this art have addressed some of the structural shortcomings of such plastic pallets as well as the desirability of stackable and nestable systems.
For example, in U.S. Pat. Nos. 3,628,468 and 3,636,888, Angelbeck discloses plastic pallets which have restraining means for maintaining four drums in position. The bottoms of these pallets are designed to engage the tops of the drums and thus allow for stable stacking.
In U.S. Pat. No. 3,948,190, Cook et al. disclose a plastic pallet formed from an integral sheet of material. These pallets are capable of carrying four drums in a relatively fixed position and can be nested for easy storage.
Kubick, in U.S. Pat. No. 3,993,168, teaches the construction of pallets having stepped edges to allow for drums of varying diameters. This system also offers integrally formed reinforcing struts extending transversely between adjacent vertical walls to inhibit transverse deflection of the pallet.
In U.S. Pat. No. 4,000,704, Griffin describes a pallet molded from a single sheet which can serve as either a top or a bottom support tray for a shipping container. These trays can be nested to conserve space when dealing with empty trays. They also incorporate interlocking means to limit lateral shifting of one tray with respect to another when loaded in a stacked configuration.
Lawlor, in U.S. Pat. No. 4,263,855, discloses a molded nesting pallet for barrels or drums having four-way entry so as to position the tines of a fork-lift truck essentially below the centers of gravity of the individual barrels or drums. The load bearing surfaces of the pallet are provided with channels which aid in the proper positioning of the cylindrical containers.
U.S. Pat. No. 4,516,677 to Rowland et al. teaches a pallet fashioned from a moldable material for transporting yarn packages having tubular cores. The pallet includes a repeating pattern of nubs upstanding from its top surface and a repeating pattern of depressions in its bottom surface which tracks the nub pattern. The nubs and depressions receive the tubular cores. The top and bottom pallets thus cooperate with the yarn package cores to provide a stable unit.
Bowser et al., in U.S. Pat. No. 4,838,176, disclose plastic foam pallets which are stackable or nestable by rotating alternate pallets 180.degree. about a vertical axis perpendicular to the loading surface.
Although the above cited art teaches plastic pallets having various advantages over traditional wood pallets, it has been found that many of these systems simply do not satisfy the strength and rigidity requirements of the chemical industry. For for example, chemical barrels typically weigh upwards of 500 pounds. Four such barrels are generally loaded on one pallet and two or three such loaded pallets are typically stacked, one on top of the other. The effect of lateral vibrations sustained during shipping, superimposed on the already high stress experienced by the bottommost pallet of such a stacked configuration, is often excessive for some of the above designs. Deformation of the plastic pallets under such loads, even when insufficient to result in complete buckling thereof, can permit transported drums or barrels to shift and contact each other or the sides of trailers, for example. Such contacts often result in damage to the drums or barrels, particularly in the case of containers having reinforcing chines which are vulnerable due to their protruding surfaces. To a degree, of course, these concerns can be addressed by fabricating the pallets from thicker gage sheets, which improves their rigidity. However, such an approach can result in a plastic pallet which is not only expensive and too heavy for facile handling, but one which also extracts a high societal cost by depleting a non-renewable resource.
Furthermore, empty barrels must often be transported in chemical industry operations (e.g., new barrels sent to a manufacturing site or return of empty ones to original supplier for refill). These barrels are also susceptible to damage due to vibrations sustained during shipping of stacked barrel/pallet combinations. Unlike the situation when filled barrels are shipped and pallet deformation can result, the reduced weight of the empty barrels actually contributes to their mutual collisions and the barrel/pallet combinations typically have to be banded and/or shrink wrapped with spacers inserted between barrels in order to prevent damage from barrel-barrel contact and/or exposure to the environment.